CHICAGO — How much longer can this go on?

That was the prevailing thought watching the Vikings stumble around aimlessly on offense Sunday night against the Chicago Bears. And you can't even pin it all on Donovan McNabb this time.

Oh, McNabb still had a few moments that made you shake your head, but everybody on that side of the ball had a hand in one of the ugliest displays of offense you'll ever see.

Facing one of the NFL's worst-ranked defenses that had two new starting safeties and wasn't exactly brimming with confidence, the Vikings managed three points, 22 rushing yards and seven first downs in the first half.

They trailed 26-3 at halftime and made enough mistakes to last a lifetime.

The second half wasn't much better as the Vikings limped out of Soldier Field with a 39-10 loss.

It's amazing that an offense featuring Adrian Peterson, Percy Harvin and Visanthe Shiancoe can look so alarmingly inept and predictable. But it did for a variety of reasons.

So here's the question: What exactly is this team's identity on offense, other than hope and pray Peterson can save the day? They don't have a Plan B when a team stuffs the run the way the Bears did Sunday night.

"We had some things we wanted to answer with in the passing game," coach Leslie Frazier said. "We just couldn't get in sync. If you get in a position where you have to throw, then we've got to be able to make some of those throws and be able to protect the quarterback. We weren't able to do that."

Fans are clamoring to see rookie Christian Ponder, but honestly, it won't matter who plays quarterback if the line doesn't perform significantly better. The Bears controlled the line of scrimmage and generated five sacks and a ton of pressure.

Ponder saw his first NFL action in garbage time, but we have no idea if he's ready to take the reins for good. Let's be honest, though. This season is going nowhere, and at some point the Vikings need to see what they have in Ponder. The time is right for a change.

Frazier did not guarantee McNabb will remain the starter going forward.

"We have to sit down Monday and talk about a lot of things and decide what direction we want to go," he said.

Frazier has shown unwavering loyalty to McNabb so far. Frazier even told a Sports Illustrated reporter last week that the media are being unfairly harsh toward his quarterback.

"It's not justified what happens to him in the media," Frazier told SI. "Some of the shots that are taken at him are just unfair. They're just not right. But he's a strong guy. He handles it very, very well."

McNabb got testy last week when reporters continued to ask about possible flaws in his mechanics, saying that topic is "getting out of hand." He actually completed 15 of 19 passes for 138 yards in the first half, but his misses were so off the mark that it felt worse.

He threw his first pass to Shiancoe high and a little behind him. Incomplete.

McNabb tried a quick screen to Harvin on his second attempt, but cornerback D.J. Moore read it perfectly and nearly intercepted the pass for what would have been an easy walk-in touchdown. He also fired a few of his patented low throws and one-hoppers.

McNabb has become an easy target for criticism, but he also got little support around him Sunday.

"Always open" Bernard Berrian dropped a pass on third-and-5.

With the Vikings backed up at their 7-yard line, center John Sullivan whiffed on nose tackle Stephen Paea and then Peterson missed him, too, enabling Paea to sack McNabb in the end zone for a safety.

Wide receiver Michael Jenkins had a false start as the Vikings lined up to go for it on fourth-and-3 at the Chicago 15. The penalty forced the Vikings to attempt a field goal, but the usually reliable Ryan Longwell hooked a 38-yarder.

Peterson rushed for only 39 yards on 12 carries. And the line was so shaky that the Vikings had little chance to succeed running or throwing.

Let's not forget, too, that the Bears were ranked 29th in the NFL in total defense. Didn't matter. Not against this offense.

"There is no other way to put it than it was ugly," Jenkins said.

That pretty much summed it up.

Chip Scoggins • ascoggins@startribune.com